What is a API?

Answer 1

API stands for "Application Programming Interface", It's allow external programs to make requests to the one provides such interface. API allow many other applications and software to use services and information from API provider. One program request for information and other returns the required data. Generally and minimally, the "published" public methods provided, some would even allow objects being referenced / copied between this service provider and the one making requests.

For example, a program would have 100 methods (and some other internal functions) to do some service for you, to use any of those 100, you must know what it can do for your program and how to make a request to that method/function. These element (name, data type, functionality, etc) composed as an API

Answer 2

APY is an accounting term that stands for Annual percentage yield, which is a normalized representation of an interest rate, based on a compounding period of one year.